Taenidium and Associated Ichnofossils in Fluvial Deposits, Cretaceous Tuscaloosa Formation, Eastern Alabama, Southeastern U.S.A

Abstract

Exposures of the Tuscaloosa Formation in eastern Alabama (U.S.A.) provided an opportunity to examine ichnofossils and ichnofabrics within Cretaceous fluvial facies. Floodplain mudstones are completely bioturbated and dominated by backfilled burrows most allied with Taenidium serpentinum. These burrows likely reflect the work of insects or oligochaetes that occupied soft, moist proximal floodplain substrates. Although the affinities and ethology of the tracemakers and the precise environmental conditions that prevailed during burrowing cannot be confidently inferred, Tnenidium‐dominated ichnofabrics of the mudstones can be assigned to the Scoyenia ichnofacies in the narrower sense of several recent authors (e.g., Buatois and Mángano, 1985). Ichnofossils are rare to absent in Tuscaloosa sandstones. The tops of some thin crevasse‐splay sands within mudstone‐dominated intervals were intensely disrupted by Taenidium producers. Large, vertically extensive, chambered(?) burrow systems, presumably dug by some unknown vertebrate organisms, locally were excavated in abandoned channel sands. In situ ichnofossils apparently are absent altogether in conglomeratic fades. However, intraformational conglomerates in channel‐fill sequences locally are composed almost entirely of Taenidium backfill segments that survived erosion from semi‐consolidated floodplain muds and subsequent fluvial transport and, thus, represent a form of concentration‐type ichnofossil‐lagerstätte.